1. Field of the Invention
The present invention relates to a process for preparing a tertiary amine having a long-chain alkyl group or groups and, more particularly, to a process for preparing a tertiary amine having one or two long-chain alkyl groups by the catalytic reaction of a long-chain olefin, carbon monoxide, hydrogen, and a primary or secondary amine.
2. Description of the Prior Art
Higher amines having a long-chain alkyl group or groups and derivatives thereof are useful, because of their structure, in a variety of applicatons such as intermediates for emulsifiers, rust inhibitors, and fabric-softeners and finishing agents, and the like. At present, most of them are commercially produced from natural fatty acids such as coconut oil, palm oil, beef tallow, and the like.
On the other hand, it is also known that tertiary amines can be synthesized from long-chain olefins, carbon monoxide, hydrogen, and primary or secondary amines. For example, Japanese Patent Publication No. 9527/66 discloses a one-stage process for preparing a tertiary amine from an olefin, carbon monoxide, hydrogen, and a secondary amine by using a catalyst comprising tri(hydrocarbyl)phosphine and cobalt carbonyl. However, this process is not necessarily effective for preparing the desired tertiary amines because it concurrently produces a large amount of alcohol as a by-product.
Helvetica Chimica Acta. vol. 54 (1971), pp. 1440-1445 and U.S. Pat. No. 3,947,458 each disclose a process for producing amines from an olefin, carbon monoxide, water and a nitrogen-containing compound using a catalyst composed of pentacarbonyliron and a rhodium compound. This process provides amines in considerably high yield, but it requires pure carbon monoxide as a reactant instead of a cheap gaseous mixture of hydrogen and carbon monoxide. It also requires the recovery of expensive rhodium compound.
Japanese Patent Application (OPI) No. 88812/74 discloses a process for producing tertiary amines by reacting an olefin, carbon monoxide, hydrogen and a secondary amine in the presence of a complex of a Group VIII metal complexed with a ligand containing an electron-donor atom such as oxygen, nitrogen or sulfur. This process also provides desired amines in extremely good yields, but problems with it in industrial practice center on the recovery and re-use of the expensive Group VIII metals rhodium and ruthenium which are used in considerably large amounts.
The reference provides no discussion of the problems with this reaction. That is, in processes for synthesizing higher amines having at least one long-chain alkyl group from long-chain olefins, the use of comparatively inexpensive cobalt or other Group VIII metals results in such a low reaction selectivity that the desired amines are produced only in low yields, whereas the use of expensive metal compounds such as rhodium compounds is so costly that it is not necessarily advantageous from an industrial point of view though it provides amines in high yields.
Accordingly, if the one-stage industrial process of synthesizing higher amines having at least one long-chain alkyl group from olefin in high yields using an expensive catalyst such as rhodium is to be practicaly realized, techniques of recovery and re-use of the expensive catalyst must be established.
Various processes have been proposed in the past for the recovery of rhodiun catalysts used in hydroformylation reactions and the like as follows:
(1) A process in which the reaction product is separated from a catalyst by evaporation or distillation (Japanese Patent Application (OPI) No. 125103/77);
(2) A process in which product aldehyde is separated from the reaction by extraction with a polar solvent such as water (Japanese Patent Application (OPI) No. 29412/76);
(3) A process in which rhodium complex is separated by adsorption (Japanese Patent Application (OPI) No. 62936/75); and
(4) A process in which the reaction product is separated by using a membrane of, for example, silicone rubber or cellulose. Although process (1) above is applicable when the reaction product is a low-boiling lower aldehyde and when the catalyst is a rhodium complex modified with, for example, triphenylphosphine which has a comparatively high heat stability, attemped aplication of the process for the production of high-boiling higher amines, the end products of the present invention, results in many problems. Process (2) described above cannot be applied to higher amines having only a low water solubility. Adsorption process (3), when applied to an industrial process for the production of higher aldehydes, is not effective for producing nitrogen-containing compounds such as amines which can adversely affect the adsorbent. Further, process (4), which utilizes membrane separation, requires that the difference in molecular size between the reaction product and the catalyst complex be sufficient, and it is not effective for separating higher amine products having a comparatively large molecular size.
In order to advantageously practice the one-stage process of preparing tertiary amines having at least one long-chain alkyl group from olefins on an industrial scale, it is necessary that techniques be established for the recovery of expensive catalysts such as rhodium by which the end product is obtained in high yield, from a reaction product for re-use. However, it is not possible to avoid decomposition or loss of portions of the expensive complex during the treatment. The amount of the decomposed or lost catalyst, even a trace amount, has a serious affect on catalyst cost in the case of expensive Group VIII metals such as rhodium. Moreover, the amount of decomposed or lost complex catalyst usually increases as its concentration increases. Accordingly, the reaction is desirably conducted at as low a catalyst concentration as possible. However, when a rhodium-containing catalyst such as RhCl.sub.3.3H.sub.2 O is used as the catalyst, the presence of the catalyst in decreased concentration results in a decelerated reaction, which in turn results in a decreased conversion of olefin and, in addition deterioration of reaction selectivity. Thus, aldehydes, intermediates of the end products of tertiary amines, are produced in large quantities in the reaction zone. This results in a sharp increase in the amount of heavy substances formed upon condensation of the aldehydes or it results in the production of large amounts of impurities such as amines having unsaturated alkyl groups or imines having carbon-nitrogen double bonds other than the desired amines. Therefore, there is no advantage to be gained by decreasing the rhodium concentration in the reaction, and it is necessary to keep the rhodium concentration at a definite level in order to avoid decreases in reaction selectivity. A need therefore continues to exist for an improved technique of recovering and reusing expensive noble metal catalysts used in the synthesis of tertiary amines.